1. 11/12/2015NASA-JSC and DIAS1 Study of Sensitivity Fading of CR-39 Detectors during Long Time Exposure D. Zhou a, b, D. O’Sullivan c, E. Semones a, N. Zapp a, E.R. Benton d a Johnson Space Center - NASA, 2101 Nasa Parkway, Houston, TX 77058, USA b Universities Space Research Association, 3600 Bay Area Blvd, Houston, TX 77058, USA c Dublin Institute for Advanced Studies, 5 Merrion Square, Dublin 2, Ireland d Eril Research Inc., 1110 Innovation Way, Suite 100, Stillwater, OK 74074, USA

2. 11/12/2015NASA-JSC and DIAS2 The Role of CR-39 Detectors in Space Studies Measurement of (1)LET (Linear Energy Transfer) (2) Dose and Dose Equivalent (3) Charge Spectrum of GCR

3. 11/12/2015NASA-JSC and DIAS3 Radiation Field in Low Earth Orbit GCR (Galactic Cosmic Rays) Solar Energetic Particles SAA (South Atlantic Anomaly) Albedo Neutrons

4. 11/12/2015NASA-JSC and DIAS4 Radiobiological Impact on Astronauts Dominated by high LET (≥ 5 keV/µm water) CR-39 detectors are most appropriate

5. 11/12/2015NASA-JSC and DIAS5 Some Space Missions Which Employed CR-39 Detectors LDEF (5.8 Years) EUROMIR (6 Months) Matroshka-1 (616 Days) Matroshka-2 (367 Days) ISS Expeditions (> 6 Months) DOBIES (15-400 days)

6. 11/12/2015NASA-JSC and DIAS6 Photo of Matroshka in Space

7. 11/12/2015NASA-JSC and DIAS7 Fading of CR-39 Sensitivity Was observed for all CR-39 detectors with long time exposure. Compared to TEPC data, results measured with CR-39 are low. Results must be corrected for fading of latent tracks irrespective of source. Use “Fe peak” of exposed detector events compare with accelerator data.

8. 11/12/2015NASA-JSC and DIAS8 A correction formula was found: S c = S o /(1-(a+bT)) where S o = etch rate ratio before correction S c = corrected value of etch rate ratio S c1 = S o1 /(1-(a+bT 1 )) S c2 = S o2 /(1-(a+bT 2 )) for exposure times T 1 and T 2

9. 11/12/2015NASA-JSC and DIAS9 Table 1: Fading Comparison for different exposure time T(a + bT)1 – (a + bT)Sc/So (Month) 60.02420.97581.0248 120.03880.96121.0404 240.06820.93181.0731

10. 11/12/2015NASA-JSC and DIAS10 Major / Minor LET before Correction LET after Correction (µm)(keV/µm water) Matroshka-1 33.3 / 23.3 39 / 7 115.45 116.04 135.83 136.47 33.8 / 21116.88137.38 36.5 / 17 38 / 21 118.05 117.20 138.64 137.72 ISS-Expedition 12 37.5 / 20.7128.5136.82 37.7 / 12129.76138.12 Table 2: Comparison of LET before and after correction of CR-39 sensitivity

11. 11/12/2015NASA-JSC and DIAS11 Table 3: Radiation measured without and with fading correction for CR-39 sensitivity (values include background) Mission (Time) Exposure Position Absorbed Dose (≥10keV/µm water) Dose Equi. (ICRP60) (≥ 10 keV/µm water) Q Factor (Days)(mGy)(mSv) Matroshka-1 (616) P1 Eye Stomach R1 R2 29.90^/ 36.94* 14.94 / 21.60 14.96 / 18.89 13.90 / 17.93 13.85 / 17.55 270.97^/ 437.00* 176.59 / 274.82 156.95 / 246.13 148.74 / 217.31 135.29 / 215.04 9.06^/ 11.83* 11.82 / 12.72 10.49 / 13.03 10.70 / 12.12 9.77 / 12.25 Matroshka-2 (367) P1 Eye Stomach R2 10.86 / 12.90 9.13 / 10.99 8.40 / 9.66 11.23 / 12.97 121.10 / 150.66 106.88 / 134.48 96.23 / 118.82 123.85 / 152.16 11.15 / 11.68 11.71 / 12.24 11.46 / 12.30 11.03 / 11.73 Expedition 12 (190) TEPC TESS SMP327 SMP442 5.31 / 6.19 4.92 / 6.22 5.31 / 6.83 7.99 / 10.59 60.06 / 69.03 59.21 / 68.89 68.98 / 78.48 89.05 / 105.61 11.32 / 11.15 12.04 / 11.08 12.98 / 11.49 11.14 / 9.97 Expedition 13 (183) TEPC TESS SMP442 4.90 / 6.23 4.55 / 6.18 7.98 / 9.31 65.33 / 74.20 64.09 / 73.39 94.90 / 109.95 13.33 / 11.91 14.09 / 11.88 11.89 / 11.81

12. 11/12/2015NASA-JSC and DIAS12 Table 4: A comparison of radiation quantities measured with JSC-TEPC and CR-39 (Fading correction applied to CR-39,ICRP60) Space Mission Absorbed Dose (TEPC / CR-39) Dose Equivalent (TEPC / CR-39) Q Factor (TEPC / CR-39) (µGy/d)(µSv/d) Expedition 1231.70 31.39346.56 / 348.1810.93 / 11.09 Expedition 1331.31 / 30.54356.58 / 359.9711.39 / 11.79 Matroshka-2 (R2)~ 34 / 33.08~ 390 / 388.3911.47 / 11.74

13. 11/12/2015NASA-JSC and DIAS13 Charge Identification (G-Seff Method) For two points separated by  x and with etch rate V T1 and V T2, G and Seff are: S eff = V eff / V g Where Vg is the bulk etch rate and Veff, the effective etch rate is For a track with 2n equally spaced etched cone, the overall value of G is given by: And the overall value of Veff is

14. 11/12/2015NASA-JSC and DIAS14 Figure: Charge identification with G-Seff method for test events.

15. 11/12/2015NASA-JSC and DIAS15 We wish to thank all those who assisted us in the ISS, Matroshka and Dobies space missions. DIAS wishes to thank the ESA PRODEX office for support of this work.